[clang] Support MemProf on darwin (PR #69640)

[Snehasish Kumar via cfe-commits]

https://github.com/snehasish requested changes to this pull request.

It would be nice to split this patch into at least two parts:

1. Add basic support for Darwin (malloc implementation, build ids, raw format etc)
2. Record and dump references to static data in the binary

I think there are a number of places where we assume x86-ELF and I would like to make sure we address any issues before adding more functionality.

https://github.com/llvm/llvm-project/pull/69640